This invention relates to aircraft autopilot systems, as well as to aircraft systems designed to cope with catastrophic loss of cabin air pressure.
On Oct. 25, 1999, Payne Stewart, one of the best players on the Professional Golf Association (PGA) tour, with victories in 18 tournaments around the world, including three major championships, died along with five other individuals after the cabin of the eight-passenger Learjet Model 35 in which they were flying apparently abruptly lost cabin pressure as the aircraft was climbing to a cruise altitude of 39,000 feet. After all aboard lost consciousness, the eight-passenger twin-turbofan business jet continued to fly a heading maintained by its autopilot for some 1,500 miles until the fuel on board was depleted, whereupon the plane plummeted to earth at high speed.
At or near an altitude of 40,000 feet, incapacitation occurs almost immediately if cabin pressure is lost. In aviation jargon, there is a term known as xe2x80x9ctime of useful consciousness.xe2x80x9d It is the measure of the time the body can cope without oxygen, and it diminishes in almost direct proportion to the increase in altitude. At 20,000 feet, the time is 10 minutes; at 26,000 feet, it is two minutes; at 30,000 feet, it is 30 seconds; and at 40,000 feet, it is 15 seconds. At the higher altitudes, irreversible brain damage is quickly followed by death. It has been speculated that if decompression of the accident were due to a blown-out window, not only would decompression have occurred almost immediately, but the temperature within the cabin would have dropped almost as rapidly to 50 degrees Fahrenheit below zero.
The death of Payne Stewart and his colleagues were not the first attributable to cabin decompression. It has been reported that some military pilots have died after blacking out from the lack of oxygen at high altitudes. However, the best-known incident dates back to Jan. 10, 1980, when Louisiana State University football coach Bo Rein and his pilot were killed in a crash reminiscent of the Payne Stewart tragedy.
Rein""s aircraft, a Cessna Conquest, departed Shreveport, La. for what was to have been a short hop to Baton Rouge. During the flight, controllers lost contact with the pilot. The plane climbed to 41,000 feet, heading on a straight-line course to the Virginia coast. Military jets intercepted the Cessna, but pilots could see no signs of life within the cabin-only the glow of the instrument panel""s indicator lights. Three and a half hours after the flight began, the plane fell out of the sky and crashed into the Atlantic. No debris or remains were recovered. Although the National Transportation Safety Board was unable to ascertain the cause of the crash, the events were consistent with a loss of cabin pressure.
What is needed is an aircraft recovery system that will prevent tragedies such as those recounted above.
The present invention provides an emergency control system for an aircraft to recover from a catastrophic loss of cabin pressure even if the pilot becomes incapacitated before he is able to activate an emergency oxygen system.
For one embodiment of the invention, an automatic pilot (autopilot) system is programmed for rapid descent, in response to a cabin depressurization condition detected by a air pressure sensor, to a flight level where there is sufficient oxygen in the atmosphere to sustain full consciousness of the pilot. For a second embodiment of the invention, the rapid descent function may be activated by a single input of the pilot, such as depressing an activation button. For a preferred embodiment of the invention, both modes of activation are available. In the event of gradual decompression of the aircraft, it is possible that the pilot might become gradually disoriented and eventually lose consciousness without having realized the need to activate the automatic descent function of the autopilot. Therefore, it is deemed highly preferable that the automatic descent function be automatically deployable by a cabin pressurization sensor. In either case, the rapid descent function of the autopilot system is programmed to reduce engine power settings to a minimum and simultaneously reduce the angle of attack and put the aircraft in its maximum slip configuration, thereby placing the aircraft in a steep, but safe, dive. As the aircraft approaches a lower altitude capable of sustaining full human consciousness, the autopilot system increases the angle of attack and eliminates the slip and increases engine power, causing the aircraft to fly level at the lower altitude until the pilot retakes control of the aircraft. Airspeed during the dive is monitored so that it does not exceed the aircraft""s design limits. In calm air, the maximum safe speed is VNE. In turbulent air, that speed should be reduced accordingly. The maximum speed during the dive may be set by inputs from a turbulence detector over a fixed period (e.g., five minutes) prior to the autopilot beginning the rapid descent function. An instrument such an accelerometer (i.e., a g meter) may be used as the turbulence detector.
To prevent autopilot malfunction from creating a dangerous control situation, a short audible, visible or other sensory detectible warning given by the autopilot system prior to commencing a rapid descent is advisable, thereby providing the pilot with the opportunity to manually override the autopilot system in advance. For a preferred embodiment of the system, the autopilot is programmed to deactivate the rapid descent function at altitudes below a maximum safe altitude (MASA). The average human being cannot function well for long at altitudes in excess of 12,000 feet. Therefore, MASA is best set at or near that figure. Nearly all autopilot systems have the additional safety feature that they are physically overridable by the pilot. In other words, the forces applied to the controls of an aircraft by the autopilot system are not so strong that they cannot be easily overridden by the average person.
In order to prevent collisions of the aircraft with high-altitude terrain when the rapid descent function of the autopilot is activated, the autopilot is preferably coupled to a global positioning system (GPS) having a database in which is stored the altitude values for at least all obstacles having an altitude greater than about 1,000 feet less than the consciousness-sustaining altitude at which the system is designed to level out after diving during a rapid descent event. The GPS is equipped with a look ahead function which selects a safe low altitude route away from high-level terrain whenever the rapid descent function of the autopilot is activated. Thus, the slipping dive to a safe altitude may be coupled with one or more turns for terrain avoidance.